TOWARD PERFORMANCE-BASED SPECIFICATIONS FOR BITUMEN AND ASPHALT MIXTURES

The United States (US) spends about $10 billion per year on asphalt pavements, but the performance of these pavements is erratic. Variable performance stems from limitations of the specifications now used to buy bitumen, and from similar short-comings in the procedures used to design and construct asphalt mixtures. Current specifications are based primarily on the consistency of materials and their work-ability during construction. These specifications do not successfully control key performance features such as rutting, cracking, and fatigue. During the past five years, the US has conducted an unprecedented, intensive investigation of the performance of bitumens and asphalt mixtures. This investigation involved the application and evaluation of many new forms of chemical characterization and physical testing. It has produced a new set of tests, specifications, and design approaches that can be applied to specify bitumens and asphalt mixtures, the reliability of which can be predicted. The new bitumen tests are based on stiffness properties measured with a dynamic shear rheometer and bending beam rheometer. The asphalt mixture tests use gyratory compaction to produce specimens, and apply a new shear-testing device and an indirect tensile creep test to estimate rutting and fatigue susceptibility. The application of the new performance-based specifications requires new laboratory equipment and training. US state and federal agencies, suppliers, and contractors are moving quickly to apply these new procedures.